The effects of resource availability on territorial behavior of the Ruby-throated Hummingbird (Archilochus colubris).

Abstract

Ruby-throated Hummingbirds (Archilochus colubris) often migrate to their summer breeding grounds, sometimes before their main food source, nectar from flowers, becomes available. On Douglas Lake at the University of Michigan Biological Station, Pellston, MI, we explored how resource availability affected aggressive behavior in hummingbirds. Eight lakeside sites had either a single or triple set of hummingbird feeders. We predicted that the richness of a resource site would determine the number of aggressive interactions initiated by males, with the more resource-rich sites experiencing higher frequencies of male-initiated territorial behavior. We also hypothesized that males would express more territorial behavior (chases and vocalizations) than females. We counted two types of territorial behavior in both males and females: chasings and vocalizations. Our results showed that more male aggression occurred at the resource-rich triple feeder sites, but there were more instances of female aggression than male aggression, especially at single feeder sites. Resource availability of a given site seems to be a determining factor affecting the distribution of each sex. I